1. Field of the Invention
The invention relates to compositions for the treatment of dentinal hypersensitivity and methods for treating dentinal hypersensitivity.
2. Description of Related Art
Dentinal hypersensitivity can cause pain and discomfort when hypersensitive teeth are subjected to changes in temperature, pressure or chemical action. Without wishing to be bound by theory, a possible source of the hypersensitivity is that dental nerves are overexposed to oral stimuli through exposed tubules in the dentin of affected teeth. Dentin is a bony material in teeth that is usually covered by enamel above the gum line and cementum below the gum line. Enamel is very resistant to degradation when compared to cementum, and recession of the gums, periodontal disease and improper dental care can expose the cementum to hostile conditions in the mouth. The enamel or cementum may be removed through decay, injury, disease or other reasons, thereby exposing the dentin to external stimuli in the mouth.
Dentin generally contains channels, called tubules, that allow material and energy transport between the exterior of the dentin and the interior of the tooth where the nerve is located. One theory of dentinal hypersensitivity, called the hydrodynamic theory, suggests that exposure of these tubules to external stimuli can cause irritation of the nerve and lead to the discomfort of hypersensitivity. Although the exact mechanism of hypersensitivity is still under investigation, it has recently been shown that pain triggered by air currents is related to the number of exposed tubules per unit area of dentin. According to the hydrodynamic theory of dentin sensitivity, mechanical and thermal stimuli of the dentin surface induces mass or energy transport through the intratubular fluid. Such fluid movements induce pain in the intradental nerves located near the dentin/pulp border.
Treatment of hypersensitivity has usually taken the form of topical delivery systems, such as dentifrices, mouth rinses, gels and sealants. One long-time treatment has been a dentifrice containing strontium chloride as the active ingredient.
The hydrodynamic theory of hypersensitivity suggests that hypersensitivity may be treated by making the nerve in the tooth less sensitive to stimuli or by blocking or occluding the tubules to prevent or limit exposure of the nerve to external stimuli. Agents to make the nerve less sensitive are generally referred to as "nerve agents," and agents that fully or partially occlude tubules are referred to as "tubule blocking agents."
One way that nerve agents work is to interfere with the electrolyte balance near the nerve. The outer membranes of the nerve then do not "fire" as frequently or as strongly as an untreated nerve. Such agents include potassium nitrate, potassium chloride, and potassium bicarbonate.
Occlusion of tubules is an alternative method of treatment. Occlusion can be full or partial and may be permanent or temporary. The invention relates to a successful tubule blocking agent comprising an acrylic polymer.
Acrylic polymers generally have been used for a great variety of dental applications. These uses include desensitizing agents, anticalculus agents, thickeners, binder ingredients, and the like. See, for example, U.S. Pat. No. 4,217,342 to Gaffar et al., issued Aug. 12, 1980 (anticalculus agent); U.S. Pat. No. 4,296,096 to Pierce, issued Oct. 20, 1981 (gelling agent); U.S. Pat. No. 4,645,662 to Nakashima et al., issued Feb. 24, 1987 (polyacrylic binder in a dentifrice with an aluminum carboxylate desensitizer); U.S. Pat. No. 4,002,732 to Gault, issued Jan. 11, 1977 (binder for a "speckle"); U.S. Pat. No. 4,847,070 to Pyrz et al. issued Jul. 11, 1989 (anticalculus agent); U.S. Pat. No. 4,661,341 to Benedict et al., issued Apr. 28, 1987 (anticalculus agent); U.S. Pat. No. 5,374,417 to Norfleet et al., issued Dec. 20, 1994 (potassium Gantrez.RTM. salts as desensitizers); U.S. Pat. No. 5,330,746 to Friedman et al., issued Jul. 19, 1994 (hypersensitivity agent embedded in acrylic polymer for sustained release); and U.S. Pat. No. 5,438,076 to Friedman et al., issued Aug. 1, 1995 (solidifying methacrylate for sustained release of pharmacological agent). One acrylic polymer, a polyacrylic acid having a typical molecular weight from about 450,000 to about 4,000,000 sold under the trademark Carbopol.TM., has been reported as a tubule blocking agent in U.S. Pat. No. 5,270,031 to Lim et al., issued Dec. 14, 1993.
U.S. Pat. No. 5,211,939 to Turesky et al., issued May 18, 1993, reports the use of charged polystyrene beads as tubule blocking agents, and U.S. Pat. No. 4,634,589 to Scheller et al., issued Jan. 6, 1987 and U.S. Pat. No. 4,710,372 to Scheller et al., issued Dec. 1, 1987, report the use of apatite as a tubule blocking agent.
Despite ongoing work in the field of desensitizers, there remains a strong and long-felt need for an effective tubule blocking agent that is compatible with fluorides and other conventional dentifrice ingredients. The agent must work well yet not be distasteful or exhibit an undesirable mouthfeel. The agent must be stable for the typical shelf-life of the dentifrice and should not interfere with other agents that may be present in the delivery system, such as a dentifrice.
CARBOPOL.RTM. type polymers, in particulate form, are effective in occlusion, but these materials can exhibit unpleasant organoleptic properties when incorporated into a dentifrice. In addition, these agents require a strong shearing force during processing into dentifrice formulations. Attempts to modify the organoleptic properties of CARBOPOL.RTM. polymers, in particular, by the addition of metal salts and glycols, have proven to be only partially effective in correcting these deficiencies.